Drive construction for phonographs or the like



Dec. 29, 1953 's. YERKOVICH DRIVE CONSTRUCTION FOR PHONOGliAPHS OR THELIKE Filed Aug. 30, 1949 4 Sheets-Sheet 1 INVENTOR Smou Yeax vmu I ATToN S Dec. 29, 1953 YERKOVICH 2,664,293

DRIVE CONSTRUCTION FOR PHONOGRAPHS .OR THE LIKE Filed Aug. 30, 1949 I 4Sheets-Sheet 2 INVENTOR sl YERKOVICH M.Wi Jafhd ATTO NEYS Dec.

Filed s. YERKOVICH 2,664,293

DRIVE CONSTRUCTION FOR PHONOGRAPHS OR THE LIKE Aug. 50, 1949 4Sheets-Sheet .5

'04 -i00 W//////////////I Dec. 29, 1953 s. YERKOVICH DRIVE CONSTRUCTIONFOR PHONOGRAPHS OR THE LIKE 4 Sheets-Sheet 4 Filed Aug. 30, 1949u|,l|l|IlllllllllllllIlllllllllllllllllllll! HHF I I I IHU S. U NW m 5 0V m. 7 WYWM W m 5 surface of the recording belt. [in the recording headis enabled to impress a Patented Dec. 29, 1953 ersNr OFFICE DRIVECONSTRUCTION FOR PHONO- GRAPHS OR THE LIKE Simon Yerkovich, Los Angeles,Calif., assignor to Dictaphone Corporation, Bridgeport, Conn., a

corporation of New York Application August 30, 1948, Serial No. 46,747

1 Claim.

This invention is described in relation to variable speed soundreproducing equipment and in such equipment more particularly to acommercially practicable backspacing construction by which the soundreproducing element may quickly and automatically be caused to assume aposition from which to'repeat a predetermined amount of the recordingbeing reproduced. Recording and reproducing equipment generally is wellknown and has commonly been used by typists and the like while makingWritten transcriptions of recorded material. Sometimes while making suchtranscriptions it becomes necessary to have repeated a brief portion ofthe recording. I am aware that various backspacing mechanisms foraccomplishing such repetitions have heretofore been offered. I havedevised a novel power transmitting construction which is ideallysuitedto rapid performance of intermittently desired backspacing operations Iand which is readily adaptable to other applications which Will suggestthemselves to those skilled in the art of mechanical power supply andtransfer.

In United States Patent No. 2,318,828 to Yerkbvioh and No. 2,371,116 toYerkovioh et a1. there described certain generally similar machinescapable of recording on an endless belt of paper thin pliable plasticmaterial and of reproducing the recordings made on such belts. Duringrecording, one of these belts is stretched between a pair of: pulleys,or mandrels, each of a diameter of about 2 in. in the illustrativeembodiments, mounted for rotation about substantially parallel,horizontally disposed axes spaced about 2% in. apart. known as a drivemandrel; the other is free to rotate about its axis and is known as anidler mandrel. lThe idler mandrel is yieldably mounted so as to hold therecording belt under a small amount of tension against thesurface of thedrive mandrel.

In the above-mentioned Yerkovich et a1. patent the mandrel axesofrotation are disposed in substantially the same horizontal plane. Asound recording head and a sound reproducing head are independentlyassociated with the mandrels formovement through independent paths,parallel to the axes of the mandrels and transversely with respect tothe path followed by the Thus a stylus held sound groove ontothe movingbelt. And as the belt moves, the recording head is moved transve'rselyat a low constant speed across the surnew: the 'beltso that the groovebegins .at one One of the two mandrels is driven and is side edge of thebelt and proceeds around and around the belt and finally ends at theother side edge of the belt. The speed ratios, between linear velocityof a point on the surface of the belt and linear velocity of therecording head as it travels transversely with respect to the movementof the belt, are such that the belt makes 20o complete revolutions whilethe stylus moves transversely a distance of one inch. Thus the sur faceof the recording belt, after a sound groove has been impressed upon it,bears a succession of closely spaced loops the distance from the. bottomof one groove trough to the bottom of the next adjacent groove troughbeing approximately .005 in. It is apparent, of course, that the closerthe spacing of the loops of the sound groove the greater the number ofloops that may be contained on a belt of a given size and accordinglythe greater the amount of recorded material that may be impressed uponthat belt. Mechanical complications and the finite width of the soundgroove per se set a practical limit upon the closeness of adjacentloops.

In the embodiment disclosed in the Yerkovich patent the linear velocityof apo nt on the recording belt during normal reproducing is disclosedas being on the order of '20 feet per minute. Thus, in ordinary usage.when the auditor who is listening to the recording misses a word or aphrase, she probably will not want a greater amount repeated than iscontained in a single s und groove loop on the recordin belt. And if theauditor ba kspaces the reproducing head with respect to the surface ofthe recording belt a distance, for example, of as much as of an inch itresults that she has backspaced a matter of ten sound groove loops,which is surely verv much more than she wants repeated. An error inbackspacing movement of as much as A in. will result in a repetition oftwice as much as the auditor intends.

Another complication is introduced by the fact that these machines arecommonly used to record a message at a point of origin, to relay themessage over a communication channel to a point of destination and thereto rerecord the message and repeat it to a transcriber or auditor. Forcoding purposes, and to make the most efiicient use of the communicationchannel, it is the regular practice to transmit the recorded materialover the channel at a rate several times greater than that at which therecording was made. In order to accomplish such transmission themachines are equipped with variable speed motors having a range on theorder of 10:1. Thus, a

conversation or message recorded at a rate of 150 words per minute mightbe transmitted at a rate of 1000 words per minute. And the machine atthe point of destination must be capable of rerecording at such higherrate and reproducing for transcribing purposes at a rate even below thatof the original.

It is obvious that where backspacing accuracy must be in terms of a fewthousandths of an inch, the speeds of movement of the parts must bebelow certain limits or their inertia will introduce such variancies asto render the mechanism undependable. And if the structure is designedfor efiicient operation at the higher motor speeds, a disproportionateperiod of time will be consumed by each operation when the motor isrunning at lower speeds. Thus, whereas a backspacing operation completedin one half a second might be wholly satisfactory to a typist,

a delay of even two seconds-only a 4:1 reduction in motor speed-mightafter a period of transcribing become an excessive annoyance. Areduction on the order of 4:1 for transcribing would not be unusual inthe routine conduct of business quite apart from the channeltransmission capabilities of the equipment.

Accordingly it will be understood that a satisfactory backspacingmechanism for a modern machine such as referred to not only mustaccurately backspace within a few thousandths of an inch but it mustperform its function without appreciable passage of time regardless ofthe speed setting of the main motor or drive mandrel.

Various mechanisms have been suggested and tried in the past foreffecting automatic backspacing under such circumstances. I have deviseda slippable coupling construction which will cooperate with relatedassemblies to move the reproducing head backwardly with respect i to therecording belt a distance of .005 in., or whatever distance may berequired for a given machine, and which facilitates completing eachoperation in a negligible time regardless of the number of revolutionsper minute being turned by the variable speed drive motor.

I shall describe my invention as it may be applied to a reproducingmachine of the general type disclosed in the Yerkovich et al. patent.Accordingly, in my illustrative embodiment, backspacing of one soundgroove will require a transverse movement of the reproducing head equalto the spacing between adjacent sound groove loops where there are twohundred loops to the inch. It is to be noted that the illustra tiveembodiment of the Yerkovich et al. patent is a recorder-reproducer; forsimplicity and to avoid repetition the machine which I have selected toexemplify my invention is a reproducer only. Machines which will be usedonly for reproducing omit those parts which are required only forrecording.

It is an object of my invention to provide a device of the characterdescribed having to a notable extent the characteristics andcapabilities set forth. Another object is to produce a commerciallypracticable component useful in a backspacing mechanism whichfacilitates backspacing upon demand independently of the condition ofthe main motor drive. A further objective is the provision of abackspacing structure which is both feasible in manufacture andfoolproof in operation and which will consistently give the desiredextent of backspacing. A further object is to provide a novel sort ofgear train mechanism which is useful in turning a shaft through a givenangle upon demand. Other objectives will be in part pointed out as thedescription proceeds and will in part become apparent therefrom.

The invention accordingly consists in the features of construction,combinations of elements, methods of operation, and arrangements ofparts as will be exemplified in the structure and sequences and groupsof related steps to be hereinafter described and the scope of theapplication of which will be set forth in the accompanying claims.

In this specification and the accompanying drawings I have shown anddescribed a preferred embodiment of my invention and suggested variousmodifications thereof; but it is to be understood that these are notintended to be exhaustive nor limiting of the invention but, on thecontrary, are given for purposes of illustration in order that othersskilled in the art may fully understand the invention and the principlesthereof and the manner of applying it in various forms, each as may bebest suited to the conditions of a particular use.

In the drawings: Figure 1 is a rear elevation (taken along the line l-lof Figure 2) of a sound reproducing machine of the type disclosed in theYerkovich et al. patent and in which my invention has been incorporated;

Figure 2 is a plan view (taken along the line 22 of Figure 1) of themachine;

Figure 3 is a sectional end view taken along the line 33 of Figure 1;

Figure 4 is a fragmentary view on an enlarged scale of a friction clutchassembly illustrating one form of the invention employed in the machine;

Figure 5 is a fragmentary view on an enlarged. scale of a mutilated gearassembly used in the illustrative form;

Figure 6 is a sectional view taken along the line 66 of Figure 5;

Figure '7 is a fragmentary view taken along the line 1'I of Figure 1showing a part of the backspacing gearing and related mechanisms:

Figure 8 is a sectional view taken along the line 88 of Figure '7;

Figure 9 is a fragmentary sectional view taken on an enlarged scalealong the line 9-9 of Figure 1; and

Figure 10 is a diagrammatic representation of certain of the electricalcircuits and some of the parts related thereto.

The machine shown in Figure 1 includes a machine frame 20, which maytake the form of a metal casting, and which includes a supporting plate22 rising from its right-hand end (see Figure 1) and a supporting plate24 rising from its left-hand end. A relatively heavy fly wheel 26 isdisposed in a substantially vertical-plane at one end of the machine forrotation about a horizontal axis. Fly wheel 26 is driven by a pair ofbelts 28 from a variable speed motor. For a more complete disclosure ofthe motor arrangement and of other conventional aspects of the presentembodiment not otherwise detailed herein reference should be made to thedisclosure of Yerkovich et al., Patent No. 2,371,116

The fly wheel is mounted upon a fly wheel shaft 30 (see Figure 1)journaled in supporting plate 22 and carried by the machine frame. Drivemandrel 32 is turned by means of fly wheel shaft 30; since the motorwhich drives the fly wheel is of the variable speed type the rate atwhich the drive mandrel is turned is variable in accordance with themotor speed. Ordinarily a constant speed is used throughout any onerecording, variations in .speed being employed for transcribing purposesto pace the rate of reproduction to the optimum capacity of the typisft.or auditors idler mandrel 34 .(see also Figure 2) is disposed 'for freerotation about an axis parallel to the axis ofrotation of drive mandrel'32. A recording belt 36 is placed around and stretched by .the mandrelsand as drive mandrel '32 is rotated, thebelt, which is held against thedrive mandrel by the yieldable mounting of the idler mandrel, is drivenand transfers rotation from the drive mandrel to the idler mandrel whileit .is .held smoothly taut.

A reproducing carriage 3.8 is disposed above the drive mandrel fortransverse movement with respect to the path through which the beltmoves. The reproducing carriage is slidable upon ,a horizontallydisposed carriage guide rod 48 (see Figures '.1 and 23 held betweensupporting plates 22 and 24. The carriage is caused to slide along thecarriage guide rod by a feed screw 132 (see Fi ure 1) positioned inconventional manner within the uide rod. The axis of the feed screw issubstantially coextensive with the axis of the carriage guide rod, Afeed nut, not shown but held within the carriage, meshes constantly withthe feed Iscrew so that rotation of the screw advances or backspaces thecarriage with respect to the recording belt depending upon the directionof rotation of the reed screw,

In normal transcribing the feed screw is driven from the fly wheel shaftby a gear train mechanism, to be described. Feed screw 42 is identicalto the feed screw used with therecording carriage. Hence the reproducingcarriage is advanced across the moving belt ata rate which makes itpossible for the reproducing stylus to follow exactly the soundgroovewhich was embossed in the belt by the recording stylus. In the describedembodiment the feed screw is rotated through 120 degrees while therecording belt is making one revolution. Accordingly, in order tobackspace one sound groove, the feed screw will have to be reversedthrough an angle of 120 degrees.

As shown in Figure 3, fly wheel shaft 30 drives a fly wheel gear it heldin mesh with an intermediate gear lfi on an intermediate shaft 48. GeardB is maintained in meshing relationship with a second intermediate geartil which turns a pinion 52 constantly meshed with a feed screw gear 54.The effect of this gear train is to reduce the number of revolutionsmade by the feed screw gear as compared to the number of revolutionsmade by the fly wheel shaft.

In accordance with my invention the drive relationship between feedscrew gear 54 and feed screw 42 is not positive. As shown in Figure 4,feed screw gear 54 has secured to its inner face an annular rim 56. Thisrim may be removed, if need be, by unscrewing machine screws 58. A drivefiangedu is keyed in driving relationship to feed screw 42; feed screwgear 54 is freely rotatable upon a hub 62 of drive flange 6%). Feedscrew gear 5:; is held in position upon hub 62 by rim dfirwhioh overlapsperipheral portions d-i' of flange 66. Feed screw gear so may be removedby removing machine-screws 58 so that the'gear can be separated fromannular rim iii. A spider spring til (see also Figure 3) is also'rotatably positioned on hub 62 and is normally compressed between theopposing faces of the inside ol'gear L54 andthe ouslde of flange Bil.Thus the spider spring tends to push gear 54 axially ofi of hub 52 butrim "56 prevents any separation more than that shown in Figure 4.Accordingly, feed screw gear Ed is held relatively firmly with respectto fiange BB and ordinarily the driving force impartedto feed screw gear54 by pinion 52 is transterred through flange Bil to the feed screw tocause operative rotation thereof. The feed screw is mounted .for.ro'tation'in a feed screw bearing .63 supported within .a bearingbushing l0 conventionally held within carriage guide rod Aid. Thecarriageguide rod, as pointed'out previously, is nomtotatably fixedbetween supporting plates 22 and 24- In the present embodiment there isprovided, as disclosed in Figure 3, a small self-starting motor '52 (seealso Figures 1 and 8); this motor I use, as will'be described, to effectreverse rotation of the feed screw. The motor (see Figure '2) drives aspur gear l4 mounted upon a motor countershait l6 which drives a bevelgear is held in meshing relationship with a bevel gear $3 which gear inturn'is locked to and drives a shaft 82 (see also Figure 3). A gear 84driven by shaft 82 is in mesh with and drives an intermediate gear 8&3which in turn meshes with and drives a spur gear 33 (see Figure 6). Amutilated gear a part of which is broken away in Figure 3 to showgear B8juxtaposed therebehind) is disposed coaxially with respect to gear '88and is rotated thereby.

Mutilated gear 911 is arranged to mesh with an intermediate gear 92which gear is in mesh with a backspacing gear 94 solidly secured toflange 69 (see also Figure 4). During ordinary operation of thetranscribing equipment a mutilated portion of gear 96, .as will bedescribed, faces gear 92 so that there is no driving relationshiptherebetween and accordingly feed screw 42 is driven through thefriction clutch between gear 54 and flange 60.. However, when it issought to effect a backspacing operation, the small electric motor 12 isenergized, as Will be described, and the train of gears includingmembers i l, 18, 80, 84, 85 and 88 comes into operation to movemutilated gear 99 into meshing relationship with gear 92 to causereverse rotation of backspacing gear 94. During thereverse movement ofgear 54 the main machine motor continues to drive the iiy wheel andaccordingly a slipping occurs betweenfiange 60 (nowmoved by gear 94) andgear 54 (driven from the fly wheel). The energizationof motor 12 is oflimited and predetermined duration, as will be developed hereinafter, sothat the reverse movement of backspace gear 94 extends through degrees.As will be described, gear 92 is then again unmeshed from mutilated gear90.

It is to be observed that the fly wheel turns at its ordinary speedwhether a backspacing operation is occurring or not and accordingly thetrain of gears which ordinarily drives the feed screw continues tooperate at itsnormal rate of speed. When a backspacing operation iscalled for, how ever, the drive is broken at the frictional coupling andthe backspacing mechanism takes precedence as it meshes with moving gear92 to effect the intended backspacing operation.

Because normal fly wheel operation is uninterrupted some provision mustbe made for enabling the backspacing mechanism to be meshed into thedrive to the feed screw. Since there is no interruption of the mainmotor, it is obvious that "ordinary gearing, Geneva mechanisms, and

the like would jam unless the engaging. parts happened by chance to fallinto mesh. It is equally evident that the backspacing movement must beof a measured amount which can invariably be imposed at will upon thenormal drive and which will be independent of the speed adjustment atwhich the normal drive is running. As disclosed and claimed in theapplication of Charles L. Bossmeyer, Serial No. 773,823, filed September13, 1947, the mutilated gear may be made to mesh properly with gear 92each time power is supplied to the backspacer motor by providing themutilated gear with a flexible feeler 95 which is clamped in place by aclamp screw 98 on the peripheral portions of gear 9%. The feeler isformed in the present embodiment from stiff wire similar to piano wireand has a cross sectional diameter which is approximately equal to thechordal thickness of one of the teeth of the mutilated gear. The feeleris provided at its outer end portion with a detent I38 (see Figure 6)formed by a right angle bend in the wire. The axis of this detent issubstantially parallel to the axis of rotation of the gear. The feeleris so adjusted and held in place by clamp screw 98 that detent Iiliioccupies approximately the region in space that would be occupied by theworking part of a tooth of gear 98 if there were another tooth beyondtooth I02. Actually, the detent is adjusted so as to extend slightlybeyond the outside diameter of the toothed portion of the mutilatedgear. In addition, the detent is spaced from tooth I82 slightly morethan the normal spacing between two adjacent gear teeth. The locationshown of clamp screw 98 with respect to tooth I02 and the configurationof feeler 96 are such that as the mutilated gear rotates toward meshingrelationship with gear 82, the first contact made is between detent I06and some tooth portion of gear 82. With the arrangement shown, theinherent flexibility of feeler 96 is such that even if the detent shouldin the first instance be squarely abutted against an outer end of atooth, the detent will yield inwardly toward the center of the mutilatedgear and, as the approaching gears tend to move at different peripheralrates, will find its way into the solid line position illustrated inFigure 6 between two of the teeth of gear 92. When the detent assumesthe location illustrated, gears 93 and 92 are oriented so that the rigidteeth will mesh perfectly. Thus, no matter what the angularrelationships between and peripheral speeds of the unmeshed gears maybe, when a driving force of rotation is applied to the mutilated gear;ieeler 38 and detent I automatically align the teeth of gears 90 and 82so that they are brought into proper mesh. Gear 90 is relieved by aclearance groove I04 across its edge into which the detent may uponoccasion enter.

When a backspacing operation is called for, the feed screw must beturned backwardly rapidly through 120 degrees. Hence, gear $2 must berotated through a finite number of degrees and to do this there must bea certain number of teeth in the toothed portion of. the mutilated gearin order that gear 92 shall be turned through the correct angle. In theembodiment here described (see Figure 3) the mutilated gear is pro:vided with two toothed portions, each' portion having ten teeth, andeach portion is provided with an advance feeler 96 carrying a detentIilii. The detent serves as an additional tooth, making eleven operativeteeth on each side of the gear. And the mutilated gear must be turnedthrough degrees.

180 degrees to bring the eleven effective teeth of one of its toothedportions into and out of mesh with the opposing teeth of gear 92 so asto turn the feed screw backwardly through 120 Thus with a singlebackspacing operation, eleven teeth of gear 92 are caused to reverse thedirection of normally ineffective backspacing gear 94 (see also Figure4) The friction clutch between feed screw gear 56 and backspacing gear95 has a damping effect on any overrunning which might otherwise occurfrom the inertia of the parts so that when the eleven teeth of gear 92have done their work there is a clean break from the backspacingmovement and gear 94 now finds itself displaced backwardly through thefriction clutch an accurately measured, predetermined amount. The feedscrew also, of course, has been turned back, through the same measuredamount. The over-all time cycle required for a complete operation andthe amount of feed screw reverse displacement remain constant under allconditions and are accomplished independently of the speed at which thevariable speed motor is turning.

The backspacing gear train is such that for one half a revolution ofcountershaft H5 there follows a one-half revolution by the mutilatedgear. One end of countershaft It carries a timing cam Hit (see Figure8). Cam IE6 is provided with a pair of diametrically spaced dwells I08.During ordinary transcribing operation, a foot IIU. of a normally openshort travel limit switch I I2 occupies the space within one of the camdwells Hi8. When the backspacer motor circuit is closed, however, andcountershaft I6 is caused to rotate, therise on cam I06 comes intoengagement with foot Ill! and switch I I2 closes a holding circuitwhich, once closed, remains closed until motor 12 has turnedcountershaft i6 through 180 degrees again to present a dwell I03 to footIII] so as to enable holding switch II2 to open and die-energize thebackspacer motor circuit. Thus, a momentary closing of the backspacermotor circuit suifices to initiate movement of countershaft I6 andthereafter, through the action of holding switch IIZ, the backspacermotor continues automatically to operate the exact length of timerequired not only to turn countershaft I6 through 180 degrees but alsoto turn mutilated gear 90 through 180 degrees and accordingly to turnfeed screw 42 backwardly through degrees. During such operation of thebackspacer motor and by virtue of my frictional coupling the variablespeed motor continues to operate in its normal direction. The backspacermotor need not be powerful for it has to overcome only the inertia of asmall part of the record drive plus the force required to make thecoupling slip. This force can, of course, be kept small; it issubstantially less than the inertia force of the remaining parts of therecord drive against which the coupling insulates the backspacer motor.As soon as the backspacer motor has caused the feed screw to reversethrough 120 degrees ordinary transcribing motion is restored to the feedscrew automatically and without pause.

When feed screw 42 is reversed, reproducing carriage 38 is caused tomove to the left, as shown in Figure 2, by one sound groove loop. It isdesirable that the reproducing stylus which ordinarily'rides in thesound groove be lifted from the surface of the recording medium whilethe reproducing carriage is being backspaced. The application of ArthurW. Skoog, Serial No. 46,752,

filed August 30, 1948, discloses and claims mechanism whichautomatically synchronizes with a backspacing operation to lift thestylus of the reproducing carriage off of the surface of the recordingmedium at the beginning of a backspacing operation and to set it downgently at the end of a backspacing operation.

Gears 88 and 90 are located upon a shaft II 3 (see Figures 2 and 3).This shaft includes an extended portion I It which reaches behindreproducing carriage 38 even when this carriage is in its extremeright-hand position. Portion III; throughout its length behind the pathof travel of the reproducer carriage has a non-circular cam-like crosssection (see also Figure 9). The reproducer carriage is provided with abracket H8 (see Figure 9) which includes an opening I20 through whichcam-like portion II6 extends. Bracket H8 serves as a pivot support for abell crank lever I22 (see Figure 9) normally urged by gravity in acounterclockwise direction so that its upper arm I24 bears slidably uponthe flat vertical face of portion H6 as the reproducing carriage ismoved by the feed screw during normal operation. However, when abackspacing operation is instituted and shaft I I I and its cam-likeportion H6 are caused to turn, bell crank lever I22 is caused to rotatethrough a small angle in a clockwise direction and is there held untilportion H6 is turned through 180 degrees. While the bell crank lever isheld against gravity in its clockwise position, its other arm I26 israised somewhat from the position illustrated in Figure 9 and in itsraised position it is in lifting contact with the underside of thebottom edge of the transducing cartridge I28 of the reproducingcarriage. The stylus is conventionally mounted in this cartridge and isheld elevated slightly off the recording medium during the period whilebell crank lever I22 occupies its clockwise position. It is during thisperiod that the feed screw is rotated backwardly. This constructionobviously raises and lowers the stylus with a smooth, gentle motionwhich cannot damage the delicate point.

As shown in Figure as, a normally-closed travel limit switch I30 isfixed in position near switch Hz with its switch-throwing button I32 sodisposed as to be engaged and actuated by the head of a screw I34 (seeFigure 2) mounted in the lefthand race OI the reproducing carriage. 'lheposition of screw I64 with respect to the reproducing carriage may be adusted and locked by an adjustment nut I30. Thus, when carriage 3u ismoved to its most left-hand position at the beginnihg of a reproducingoperation, screw I is brought into contact with button I52 so as to openswitch I30. With switch I30 open the circuit oi the backspacing motor isopen so that a backspacing operation cannot be instituted; switch [sowill not close until the re roducing carriage is moved Irom its mostleft-hand position. in this manner it is made impossible ior thebackspacing motor to be energized unless the reproducing carriage is ina position Irom which it may be backspaced without Jamming.

Figure indicates diagrammatically the electrical circuit of thebackspacing motor. As here shown, a backspacing operation instituted bymomentarily closing a normally open sw tch I36. Ordinarily this switchis arranged I01 loot operation. When switch I38 is closed current flowsfrom a supply line I40 through a branch line I42, switch I38, normallyclosed safety switch I30, and branch lines I I4 and I46 into motor '52,thence to a branch line I43 and back to main line I50. When switch I 38is closed motor 12 starts and cam I09 immediately operates to closeholding switch II2. Power is then available through branch line I 54 tobranch line I46 and thence through the motor and line I 48 to line I50.Thus, when the starting switch is closed, holding switch II2 assuresthat a complete backspacing operation is accomplished. When thereproducing carriage is moved to its most left-hand position, however,screw I34 comes into contact with button I32 and opens switch I30. Aslong as switch I30 is open nothing is accomplished by closing switch I38and so backspacing is prevented until such time as the reproducingcarriage is moved to a position from which it may be backspaced withoutjamming.

From the foregoing it will be seen that a backspacing structure made inaccordance with the present invention is well adapted to attain the endsand objects hereinbefore set forth and to be economically manufacturedsince the several parts and assemblies are suited to common productionmethods and are susceptible to a wide latitude of variations as may bedesirable in adapting the invention to different applications.

As various embodiments may be made of the above invention and as changesmight be made in the embodiment above set forth, it is to be understoodthat all matter hereinbefore set forth or shown in the accompanyingdrawings is to be interpreted as illustrative and not in a limitingsense.

I claim:

In a phonograph transmission system, a rotatably mounted feed screw, afirst gear-like unit keyed to said feed screw and having an annularsurface, a second gear-like unit freely rotatable upon and axiallyslidable along said feed screw and having an annular surface opposingsaid first-mentioned annular surrace, and a spider spring compressedbetween said units and Irictionaliy engaging said annular surfaces; oneof said units including portions interengaging portions of the otherunit and holding said units against axial separation by said spring.

SIMON YERKOVICH.

References Cited in the file of this patent UNITED STATES PATENTS

